alt. output question

[nrob84]

simple question, my merc 470 came with the alt. conversion installed with a delco 100 amp one wire alt installed. ive takin the boat out fishing and cruising a few time and last trip i noticed the batteries were crankng the engine slow. so i got home and tested the batteries with a midtronics digital battery analizer and found both batteries with less than 100 cca, so i replaced both batteries with deep cycle marine batt. im not sure of the age of the old ones so i checked everything just to make sure they died of old age and not something else. when i checked the alt output it is charging at an average of 15.5 volts. i know marine and cars are different animals but i am used to seeing 13 to 14 volts on the newer cars i work on at work. is this normal or high? is this high of an output going to damage the batteries? thanks for reading and any input, i really appreciate all of your help.

 

[bruceb58]

Re: alt. output question

That voltage is too high. You will boil the water out of the batteries. On the last ones that you pulled out, was the electrolyte low?

 

[nrob84]

Re: alt. output question

they were sealed duralast car batteries, looked pretty old, didnt think to check if it was low, just figured they were old i do remember hearing the fluid spash around in one when i put it in the car to return it for a core. but i didnt hear anything in the other... so i guess ill be looking for a new alt. hmmmmm i assume that is also why my coil started leaking, with it running i was getting 12 volts after the resistance wire... all makes sence now!! thanks bruce your a life saver...

 

[Howard Sterndrive]

Re: alt. output question

100 amps is pretty hard on batteries.
You want "tough" batteries for that heavy charge.
(I don't get why they make these super high output alternators for boats - 55A more than enough)

should have a 4 ga wire coming off that alternator or it will get mighty warm @ 100A output.
I might even go 2 ga.for 100A if I could find the right terminal lug to mate the cable to the alt.

You have a 100A breaker? I can't even picture a 100A red button breaker... they must exist

 

[cr2k]

Re: alt. output question

Is the one wire alt even a marine alt?

I agree 15v is a lot. 13.8 to 14.5 is common. There is no need for a 100A unit unless you are charging trolling motor batteries.

Sometimes if a little is good more is not better.

 

[nrob84]

Re: alt. output question

well the boat has 2 deep cycle batteries so they are heavy duty. it is rated at 100 amp because it can handle up to having to put out 100 amps. this doesnt mean it is constantly putting out 100 amps. it has a voltage regulator inside that controls the output. it is a marine, its a delco, very common look around on google, tons of them. i installed the same style on a hotrod i built a few years back and the instructions that came with it said to use 10 guage wire, so i did and havent had a problem yet. however this alternator has 8 guage because thats what i had in the garage. when i got the boat it had 2 12 guage wires off the output the the battery switch, all looked fine, no burns. i just didnt like the 2 wires so i replaced them.

 

[bruceb58]

Re: alt. output question

8 gauge would be fine. You will only be charging 100A for a very short time anyway, literally minutes. As the batteries get any charge in them at all, the current will taper off. You will get a bit of a voltage drop but that will also be going down fast as the current drops.

How did you measure the charge voltage? At the battery?

 

[dan t.]

Re: alt. output question

why buy a new alternator? the delco unit is one of the simplest made , a new regulator is about 20 bucks. it is identical to the automotive one, same part number. strip it down and change it,takes about 1/2 hour

 

[Howard Sterndrive]

Re: alt. output question

why buy a new alternator? the delco unit is one of the simplest made , a new regulator is about 20 bucks. it is identical to the automotive one, same part number. strip it down and change it,takes about 1/2 hour

and while you are changing the regulator on any marine delco, you can throw in a self-exciting regulator and make it a "1 wire" alt.

 

[nrob84]

Re: alt. output question

i checked the output at the battery and then at the post coming out of the alt. 15.5 at both. it already is a 1 wire alt. well i already have one coming in the mail so i guess ill put a new reg in this one and keep it just in case. you can never have to many spare parts!!

 

[bruceb58]

Re: alt. output question

Have you ever disconnected the battery while the engine is running? This would include switching a battery select switch to the off position while running.

 

[nrob84]

Re: alt. output question

nope. atleast I havent, not sure if the previous owner did, i know thats a BIG no no, ive only owned the boat for about a month and being in RI the weathor hasent exactly been great boat weathor so its only been out 3 times. however!!! now i know the alt has an issue so i wont take it out and the sun is out and its warm!!! oh well. should have the new one soon i hope!